Swallows Do Make The Spring

It's finally feeling like spring, there are at least a few flying insects around, and right on cue, these guys are arriving:

Tree Swallow (Tachycineta bicolor), Gander Mt. FP,
Lake Co, IL  5/23/2012

This is a Tree Swallow (Tachycineta bicolor). And here's a few of his relatives:

Violet-Green Swallow (Tachycineta thalassina), Garden of the Gods Park,
El Paso Co, CO 5/25/2013

This handsome gentleman is a Violet-Green Swallow (T. thalassina). They're found out west, but there are a handful of records from Illinois, including one last year from Lake County.

Northern Rough-winged Swallow (Stelgidopteryx serripennis),
Gander Mt. FP, Lake Co, IL  6/30/2012

This is a family of juvenile Northern Rough-winged Swallows (Stelgidopteryx serripennis). (Sometimes I think that scientific names have an inverse relationship to the size of the organism!) You can tell they're juveniles by the very fresh plumage and the yellow corners to the mouth. And finally, just because:

Barn Swallow (Hirundo rustica), Horicon NWR, Dodge Co, WI 8/13/2013

This is a Barn Swallow (Hirundo rustica), midflight. If you're British, you'd know this one as simply Swallow, but that doesn't work so well here in the States.

Swallows have been the subject of numerous studies -- they're fairly diverse, but not overwhelmingly so, they tend to be quite approachable, including at nesting sites, many will use artificial nest boxes or buildings, and many of them nest colonially, all useful traits from a biologist's viewpoint. A particularly interesting article from 1993 examined the evolution of nest building behavior in swallows, mapping it onto a molecularly-derived phylogeny. (1)

They found that ancestral swallows probably nested in burrows, as do modern Bank (Riparia riparia) and Rough-winged Swallows. This lineage produced two offshoots, one that utilizes already-existing cavities (often old woodpecker holes) and one that builds mud nests, in some cases hanging them from the undersides of eaves, cave mouths, etc. The authors argued that the cavity nesters are a monophyletic group that evolved in the New World (in the US it includes Purple Martins (Progne subis), Tree Swallow and Violet-Green Swallow), and that their diversification was tied to recent mountain building and the resulting diversity of forest types. Clay-nesters apparently diversified in Africa, and must have colonized the New World more recently, since Barn, Cliff (Petrochelidon pyrrhonota), and Cave Swallows (P. fulva) all build mud nests.

I find it interesting that nest-building techniques are fairly conservative -- with approximately 85 species, they only found 3 main types of nest, and each one seemed to have evolved only once. Other types of traits can evolve so quickly that this sort of analysis yields little insight, while still other traits change so seldom that there wouldn't be any variation to examine in a group so small. Before seeing this paper, I would have guessed that nest-building techniques would fall into the too quick category.

(1) Winkler, D. W., & Sheldon, F. H. (1993). Evolution of nest construction in swallows (Hirundinidae): a molecular phylogenetic perspective. Proceedings of the National Academy of Sciences, 90(12), 5705-5707.